1. Field of the Invention
The present invention relates to a touch panel.
2. Description of the Related Art
A touch panel is an input device provided in front of a display and capable of inputting data. As a user can directly input data based on information visually grasped by viewing the display through the touch panel, the touch panel is used in various ways.
A type of touch panel where a resistance film is used is known. The touch panel of this type includes an upper electrode substrate including a transparent conductive layer formed on its surface and a lower electrode substrate including a transparent conductive layer formed on its surface. The upper electrode substrate and the lower electrode substrate are stacked with the transparent conductive layers facing each other. Here, the transparent conductive layer of the lower electrode substrate functions as the resistance film. With this structure, when a force is applied to a point on the upper electrode substrate, the transparent conductive layer of the upper electrode substrate and that of the lower electrode substrate make contact so that the position where the force is applied can be detected.
For the touch panel of the type where the resistance film is used, a four-wire type and a five-wire type exist. For the four-wire type, electrodes for the X-axis direction and electrodes for the Y-axis direction are provided at different ones of the upper electrode substrate and the lower electrode substrate. For the five-wire type, both of the electrodes for the X-axis direction and the electrodes for the Y-axis direction are provided at the lower electrode substrate, where the upper electrode substrate functions as a probe to detect a voltage (see Japanese Laid-open Patent Publication NO. 2004-272722 or Japanese Laid-open Patent Publication NO. 2008-293129, for example).
The structure of the touch panel of the five-wire type will be explained with reference to FIG. 1 and FIG. 2. FIG. 1 is a perspective view of the touch panel 200 of the five-wire type. FIG. 2 is a cross-sectional view of the touch panel 200 of the five-wire type.
The touch panel 200 of the five-wire type includes a film 210 that functions as the upper electrode substrate, a glass sheet 220 that functions as the lower electrode substrate, and spacers 250. The film 210 includes a transparent conductive layer 230 formed on its surface. The glass sheet 220 includes a transparent conductive layer 240 formed on its surface. The film 210 and the glass sheet 220 are stacked through the spacers 250 with the transparent conductive layer 230 and the transparent conductive layer 240 facing each other. The touch panel 200 is connected with a host computer, not shown in the drawings, through a cable 260.
As shown in FIG. 3A, the touch panel 200 further includes four electrodes 241, 242, 243 and 244 at respective four edges of the rectangular transparent conductive layer 240 of the glass sheet 220. Here, voltage is alternately applied in the X-axis direction (lateral direction) through the electrodes 242 and 244 and in the Y-axis direction (longitudinal direction) through the electrodes 241 and 243. With such a structure, when the transparent conductive layer 230 is pushed by a finger or the like at a point A and the transparent conductive layer 230 and the transparent conductive layer 240 contact at the point A, an electric potential Va is detected through the transparent conductive layer 230 as shown in FIG. 3B to detect a contacted position in the X-axis direction and in the Y-axis direction.
However, for the above touch panel of the five-wire type, it is impossible to detect when plural positions are contacted at a same time although it is possible to detect a single contacted position.
As shown in FIG. 4A, when the transparent conductive layer 230 is pushed by fingers or the like at points A and B at a same time and the transparent conductive layer 230 and the transparent conductive layer 240 contact at the points A and B, while alternately applying voltage in the X-axis direction (lateral direction) and in the Y-axis direction (longitudinal direction), a middle point between the points A and B, which is not pushed, is detected as a contacted position. This is because the contacted position is detected by the electric potential as shown in FIG. 4B. As shown in FIG. 4B, even when the transparent conductive layer 230 and the transparent conductive layer 240 contact at the points A and B, only the electric potential Vc is detected and the contacted position is detected as a single position.
In order to solve such a problem, the transparent conductive layer 230 in a rectangular shape of the upper electrode substrate of the touch panel may be separated into plural areas to detect plural positions when plural points are pushed at a same time.
However, when separating the transparent conductive layer of the upper electrode substrate into the plural areas, there exist areas which are not positioned at the edges (periphery) of the upper electrode substrate. For those areas, extracting areas which are connected to those areas and extend between those areas and the edges of the upper electrode substrate are necessary. In such a case, the layout or the structure of the extracting electrodes needs to be considered in order to retain operational functions.